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    <title>Document</title>
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    <script>
        const map = new WeakMap();
        let key = {};
        let obj = { foo: 1 };

        map.set(key, obj);
        // obj置为空时
        obj = null;
        // 依然能通过key获取到
        console.log(map.get(key));
    </script>
</body>
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